Process for preparing BIS(ether anhydrides) using alkylamine derived bisimides having low melting temperature

ABSTRACT

A process for making bis(ether anhydrides) employs alkylamines having low melting temperatures thus allowing for novel intermediate process steps for preparing bis(ether anhydrides). The alkylamines have alkyl groups which contain at least three carbon atoms and have boiling temperatures in the range of 48 to 250° C. at atmospheric pressure. As a result of using these amines, liquid alkylamines now can be employed in the imidization process step. The N-alkyl nitrophthalimides prepared from the recovered imidization product according to this invention can now be purified using liquid/liquid extraction or vacuum distillation. The alkyl nitrophthalimides prepared according to this invention provide for displacement reactions which now can be run at a high solids level. Likewise, the exchange reaction can be run at a higher solids level, and thus achieves an efficiency level which is higher than conventional processes.

This is a divisional of application Ser. No. 08/652,067 now U.S. Pat.No. 5,719,295 filed on May 23, 1996; which is a divisional of 08/250,736filed on May 27, 1994 which issued Jul. 16, 1996 (U.S. Pat. No.5,536,846).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to processes for preparing bis(etheranhydrides). In particular, safer and more efficient imidization,nitration, displacement and exchange reactions leading to thepreparation of bis(ether anhydrides) are made possible as a result ofconducting the imidization step with a liquid alkylamine wherein thealkyl group of the alkylamine preferably contains at least three carbonatoms.

2. Brief Description of the Background Art

Processes for preparing bis(ether anhydrides) are well known. Bis(etheranhydrides) are intermediates used to prepare polyetherimides which arewell known components for plastic automobile parts and the like.Biphenol dianhydride and bisphenol A dianhydride are two frequently usedintermediates. Processes for preparing such bis(ether anhydrides) caninvolve four intermediate steps. Those process steps comprise:

(1) an imidization step in which "make-up" n-alkyl phthalimide issynthesized from an alkylamine and phthalic anhydride,

(2) a nitration step in which the n-alkyl phthalimide is nitrated,

(3) a displacement reaction step in which the nitro substituent on thephthalimide ring is displaced and a bisimide is formed, and

(4) a transformation step ("exchange reaction") in which the bisimide istransformed to dianhydride, preferably by reacting the bisimide withphthalic anhydride in the presence of triethylamine and water. Theexchange also can be carried out by a process in which the bisimide ishydrolyzed, acidified and dehydrated to form the desired bis(etheranhydride). The resulting product can then be employed to preparepolyetherimides such as ULTEMO polyetherimides commercially availablefrom General Electric Co. See, for example, U.S. Pat. No. 4,020,089 toMarkezich (imidization); U.S. Pat. Nos. 4,902,809 to Groenaweg et al.and 4,599,429 to Odle (nitration); U.S. Pat. No. 4,257,953 to Williams,III et al. (displacement); and U.S. Pat. Nos. 3,957,862 and 3,879,428,both to Heath et al. (exchange reaction).

As with many commercial chemical synthesis processes, there remains aneed and desire to improve the process from economic, environmental andoverall efficiency aspects. We have specifically identified the use ofmethylamine in the preparation of the "make-up" phthalimide as an aspectof the existing process that, if avoided, could lead to processimprovements.

The disadvantage presented by methylamine is twofold. Methylamine is notonly toxic, but also its boiling temperature is relatively low,therefore rendering it gaseous at temperatures under which make-upphthalimide is synthesized. As a result, methylamine requires specialtoxic gas equipment when preparing the "make-up" phthalimide. Inaddition, at least two condensers are typically employed to condensemethyl phthalimide to its more practical liquid form. The liquidcondensate which forms in the condenser, however, solidifies on thewalls of the condenser and creates blockages. As a result, the condenseris taken off stream and another condenser is utilized while the blockedcondenser is heated to remove the residue. The second condenser issimilarly removed once it becomes blocked. A safer and more efficientprocess thus is desired.

In addition, the resulting methyl-derived phthalimide has a high meltingtemperature and thus must be stored at temperatures of about 133° C. orhigher in order to keep the "make-up" phthalimide in liquid phase forfurther processing.

The overall efficiency of nitrating methyl phthalimide is relatively lowbecause recycling the methyl phthalimide nitrating agent requires arelatively inefficient nitration concentration system. After nitratingthe phthalimide ring to form a methylnitrophthalimide, thenitrophthalimide product and the nitrating agent are recovered. N-methylnitrophthalimide usually is recovered by removing the nitrating agentand solvent via a falling film evaporator. A falling film evaporator,however, is only capable of concentrating N-methyl nitrophthalimide toabout 50% solids. Attempts to remove any more nitric acid results in theprecipitation of the methylnitrophthalimide product from the solution.As a result, methylnitrophthalimide reaction product solution isquenched into weak nitric acid. The resulting precipitate is washed incountercurrent fashion on a belt filter. In order to be recycled forlater nitration, the remaining dilute nitric acid must be recovered in anitric acid concentrator and sulphuric acid concentrator (NAC/SAC)system. Both the belt filter and NAC/SAC system are quite inefficient asthey employ about two pounds of water for every one pound ofmethylnitrophthalimide produced.

The N-methyl nitrophthalimide product then is dried by partitioning theproduct from water into toluene. Handling environmentally hazardousorganic solvents thus is required. Organic solvents also are required inthe displacement reaction which forms the bisimide.

Further problems and inefficiencies are presented when extracting theby-products created by the displacement reaction ofmethylnitrophthalimides with the salts of sodium bisphenol. Thesebyproducts typically are extracted at temperatures of about 85° C. usingalkali solutions at concentrations of about 1 to about 5% alkali.Extractions with such solutions can cause hydrolysis of the desiredbisimide product, and as a result, the time, temperature and alkaliconcentration must be monitored in order to minimize such hydrolysis.

Displacement reactions with N-methyl nitrophthalimides also can becarried out to only about a 22% solids level in the bisimide reactionmixture. If the reaction is allowed to run to a higher solids level,bisimide product precipitates out of the solvent. In addition,substantial amounts of organic solvents are required for processingmixtures at these levels of solids. Running this reaction to a higher,and thus more efficient, solids level thus is difficult and limited.

Inefficiencies also occur in the exchange reaction with bisimidesderived from methyl amines. The reaction influent of the preferredexchange reaction comprises bisimide and excess phthalic anhydride andtriethylamine, as well as the accompanying transimidization products ofboth reactants, e.g., bisimide, imide acid, diacid, phthalic acid, andN-methyl phthalimide. By-products typically are removed by extractingthe imide products into toluene, thereby driving the equilibrium andleaving only tetra acid salts in the aqueous phase. These acid saltsthen are stripped of water and triethylamine to leave the desireddianhydride. Methyl-derived bisimides, however, have a limitedsolubility in toluene, and, therefore, throughput of reaction productsolids in the exchange reaction of these bisimides is low, e.g., about12%. Greater efficiency is desired.

SUMMARY OF THE INVENTION

The foregoing disadvantages are overcome by the present invention. Theinventive method includes the steps of (a) synthesizing an N-alkylphthalimide from (i) liquid alkylamine and (ii) liquid anhydride; (b)nitrating the N-alkyl phthalimide to produce a N-alkyl nitrophthalimide;(c) purifying the N-alkyl nitrophthalimide employing liquid/liquidextraction or vacuum distillation; (d) drying the extracted or distilledN-alkyl nitrophthalimide under substantially solventless conditions; (e)reacting the dried N-alkyl nitrophthalimide with a bisphenol alkali saltto form a bisimide wherein the solids level of the reaction is at least30% by weight; (f) hydrolyzing the bisimide to form a tetra-acid salt;and (g) acidifying and dehydrating the tetra-acid salt to form thebis(ether anhydride).

The liquid alkylamine employed in the imidization step preferablycontains three or more carbon atoms. As explained more fully below, thepresence of such an alkyl group in the various reaction intermediatesfurther improves the total efficiency of the bis(ether anhydride)preparation.

Butyl and propyl amines are preferred liquid alkylamines in someinstances because of their relatively low cost When employing acontinuous process of preparing bisimides and/or bis(ether anhydrides)substantial cost savings thus can be realized. Butyl, propyl and hexylamines are preferred when preparing biphenol dianhydrides.

One or more of the following novel process steps according to thisinvention also can be employed as an intermediate step in conventionalprocesses for preparing a bis(ether anhydride).

For example, the "make-up" phthalimide now can be prepared from liquidalkylamines, as opposed to gaseous amines, thereby alleviating the needfor the gas-handling equipment used for methylamine.

N-alkyl nitrophthalimide suitable for preparing a bis(ether anhydride)for example, can now be prepared by (a) providing a N-alkyl phthalimideand a nitrating agent; (b) removing substantially all of the nitratingagent; and (c) purifying the N-alkyl nitrophthalimide employingliquid/liquid extraction or vacuum distillation. This process thusalleviates the need to run an inefficient belt filter process. Asmentioned earlier, the belt filter process consumes substantial amountsof water. Moreover, the extracted or distilled N-alkyl nitrophthalimidenow can be dried under substantially solventless conditions, which alsoreduces the amount of water consumption during the nitration process.

Alkylnitrophthalimides according to this invention (wherein the alkylgroup has three or more carbon atoms) have a relatively high solubilityand provide for bisimide preparation reaction mixtures having a solidslevel previously not obtained with methyl nitrophthalimides. Substantialamounts of solvent thus are avoided and higher throughput ofsubstantially pure bisimide product is provided when employing thisinvention. As a result, bisimides suitable for preparing a bis(etheranhydride) now can be prepared by (a) providing a N-alkylnitrophthalimide and a bisphenol alkali metal salt; (b) reacting theN-alkyl nitrophthalimide and the salt at a solids level of at leastabout 30% by weight solids to form a substantially pure bisimide; and(c) extracting the bisimide. The bisimide also can be prepared undersubstantially solventless conditions, e.g., at a 100% solids level.

As mentioned above, any or all of these steps can be employed in abis(ether anhydride) preparation process. In the alternative, one of thesteps described above can be employed in a bis(ether anhydride)preparation process which otherwise comprises conventional steps.

DETAILED DESCRIPTION

The melting temperatures of the alkylamines employed according to thisinvention allow the phthalimide synthesis step of this invention toemploy liquid reactant The alkylamines according to this invention areliquids at ambient conditions and have boiling points in the range of48° C. to 250° C. The alkyl groups of these alkylamines contain three ormore, and preferably three to six carbons.

N-alkyl phthalimide synthesis typically is conducted at a temperature inthe range of 155 to about 170° C. Water created during the N-alkylphthalimide synthesis is removed employing conventional techniques,e.g., simple distillation at 155° C.

While methyl-substituted phthalimide is isolated and stored atapproximately 180° C. under nitrogen, the N-alkyl phthalimides preparedaccording to this invention can be stored as a melt, for example, atabout 40° C., i.e., the approximate melting point of N-butylphthalimide. The alkylphthalimide according to this invention has aformula ##STR1## wherein R is at least a C₃, and preferably a C₃ -C₆alkyl.

The choice of the number of carbon atoms in the alkyl group "R" dependson the desired reaction product, process speed and efficiencies for theparticular process being conducted. Lower alkylamines such asn-propylamine and n-butylamine are particularly preferred. The propylgroup provides for materials which are easier to purify. Thepropyl-derived products produced during nitration reactions in thepreparation of bisphenol A dianhydride, for example, are easier topurify than butyl-derived products. As discussed in more detail below,purification of butyl-derived nitration products involves additionalsteps in order to achieve a commercially acceptable impurities level.N-hexylamine is sometimes preferred when preparing biphenol bisimide.

The butyl-derived materials are more soluble in the solvents typicallyused in the various reactions. The higher solubility allows forreactions at higher solids levels and accordingly makes the processaccording to this invention more efficient. The improved solubility ofthe butyl-derived materials over propyl-derived materials is especiallyhighlighted in the preparation of biphenol bisimides. For this reason,the butyl-derived materials are preferred when preparing suchdianhydrides. The solubility of various alkyl-derived imides,nitroimide, bisimides, etc., in toluene are disclosed in Table 5. Theboiling temperatures and melting temperatures of the compounds accordingto this invention also are included in that table.

Other suitable alkyl groups include n-hexyl and t-butyl. As mentionedabove, the selection of a particular alkylamine depends on severalfactors familiar to those of ordinary skill in this field who will beable to make such selection based on the teachings herein.

An N-alkyl phthalimide prepared according to this invention is nitratedto prepare N-alkyl nitrophthalimides. The N-alkylphthalimide is nitratedusing known processes or by using the nitration process according tothis invention. Known methods of nitration are described in U.S. Pat.Nos. 4,902,809 and 4,599,429. The nitration process according to thisinvention is described below.

Suitable nitrating agents for nitrating the N-alkylphthalimide inventioninclude a nitric acid solution having a concentration of at least about94% and preferably a concentration in the range of from about 97.5 toabout 100% by weight, with the balance being water. While nitric acidsof lower concentration are useful for the nitration process, the use ofsuch concentrations results in processes which are too slow to be costeffective. Nitric acid solutions of at least 94% are availablecommercially. In the alternative, such solutions may be prepared byknown concentrating methods from more widely available commercial nitricacid of 60 to 67% concentration. The concentrated nitric acid also maybe mixed with another concentrated acid such as sulfonic acid to preparea nitrating agent suitable for this invention.

The amount of concentrated nitric acid used in the nitrating agentshould be at least a stoichiometric amount necessary to attach one NO₂group on the aromatic nucleus of the N-alkylphthalimide. Generally, theweight ratio of nitric acid to the N-alkylphthalimide should be fromabout 0.4 to about 50, preferably from about 5 to about 30, mostpreferably from about 9 to about 15. Lower or higher amounts of nitricacid also may be used in the process of the present invention. Loweramounts of nitric acid, however, result in poor yields and too slow areaction rate to be cost effective. Higher amounts of nitric acid mayresult in unnecessary decomposition of concentrated nitric acid andincreased cost for such acid and its recycling.

The N-alkylphthalimide may be added to the reactor in any suitable form,e.g., powder, flake, etc., but preferably in liquid form.

The concentrated nitric acid and the N-alkylphthalimide are mixedtogether in a reactor or reactors preferably equipped with a stirrer andmeans for heating or cooling the reactor. The reactor(s) may be such asto allow for either batch or continuous processing.

Specific variations in the design of the process systems employed topractice the nitration according to the present invention are known tothose skilled in the art For example, it is possible to use one or morereactors in series or parallel which operate in the plug flow mode withor without radial mixing and with or without heating or cooling.Alternatively, it is possible to use one or more reactors in series orparallel which operate in the back mixing mode, again with or withoutheating and cooling and operating in a batch or continuous mode.Finally, it also is possible to use a combination of reactors withfeatures of both the foregoing. The nitration reaction mixture's energycontent, especially at lower nitric acid ratios, also must be taken intoaccount when designing the process equipment.

The mode of mixing and the sequence of addition of reactants is notcritical to the present invention. Feed of the reactants may either beinto the first reactor or be portioned among the reactors if more thanone reactor is used, or they may be entered at different locations ofthe reactor or reactors. Further, the reactants may be pre-mixed beforeentering the reaction process or they may be fed separately. It also ispossible that one or both reactants are brought to the desired reactiontemperature prior to mixing or entering the reactor.

Generally, the reaction temperature should fall within the range of fromabout -20° C. to the boiling point of nitric acid, preferably from about10° C. to about 70° C., most preferably from about 20° C. to about 60°C. More specifically, the actual temperature to be employed is dependentupon the desired rate of reaction and the desired end products, e.g.,the desired ratio of the 4-isomer, i.e., 4-nitroalkyl phthalimide, to3-isomer, i.e., 3-nitroalkyl phthalimide, formed in the products.

Temperatures outside the range of temperatures disclosed above also maybe employed with the present process. However, lower temperatures resultin a reaction rate which is too slow to be cost effective, whereashigher temperatures require operation at above atmospheric pressure toprevent boiling and subsequent loss of nitric acid.

While the temperature at which the reaction is run has a significantimpact on reaction rate, the specific reactants used and the ratio ofreactants in the reaction mix also influence the reaction rate. Withrespect to the latter, the higher the concentration of the nitric acidin the initial mix or as added during continuous processing the fasterthe reaction rate. The specific alkyl group on the N-alkylphthalimidealso is found to influence reaction rate. Finally, with respect to theratio of the reactant mix, it is found that the rate of reactionincreases as the ratio of nitric acid to N-alkylphthalimide increases.The most dramatic reaction rate increase, in this respect, being notedas the reactant ratio approaches about 10.

Thus by varying any one or all of the foregoing, one may significantlyincrease or decrease the time for which the reaction should run toobtain optimum yield. In general, with a reaction run at a temperaturewithin the preferred range, e.g., 20° C.-60° C., up to about 90% orgreater yield may be obtained within three hours. Optionally, theseyields may be increased further by allowing the reaction mix to standfor a period of time prior to separation.

The pressure range under which the nitration process operates may varyfrom vacuum to above atmospheric pressure. Process and safety concernsmay dictate operating the process under slight vacuum. Such conditions,however, depend on the type of reactor or reactors employed. Otherwise,the process is generally run at about atmospheric pressure.

The desired reaction products of this invention comprise primarily the3- and 4-isomers of the respective N-alkyl nitrophthalimide. Thespecific ratio of the 3- and 4-isomers is largely dependent upon thetemperature at which the reaction is run. For example, the ratio of 4-to 3-isomer may vary from about 16:1 at about 60° C. to about 26:1 atabout 15° C. The weight ratio of starting reactants also may have aslight influence on the isomer ratio.

The ratio of 4- to 3-isomer may also affect the melting temperature ofthe N-alkyl nitrophthalimide. Compositions comprising primarily3-isomers have lower melting points than those compositions comprisingprimarily 4-isomers. The lower melting temperatures of the formercompositions, thus, make it easier to run the displacement reactionunder solventless conditions as discussed later below.

N-alkyl nitrophthalimide resulting from the nitration reaction has aformula of ##STR2## wherein R is an alkyl group preferably having atleast three carbons, and preferably having three to six carbons.

The resulting N-alkyl nitrophthalimide is recovered by first removing,for later recycle, as much nitrating agent, e.g., strong nitric acid, aspossible. When N-alkyl nitrophthalimide is prepared from a methyl amine,recovery is carried out until the reaction mixture contains about 50%solids, typically achieved by using a falling film evaporator.Subsequently, conventional processes quench the product-containingsolution into weak nitric acid and the resulting precipitate then iswashed in counter current fashion on a belt filter. The dilute nitricacid in such a system is recovered and recycled using a nitric acidconcentrator and sulphuric acid concentrator (NAC/SAC) system.Typically, two pounds of water is used for every one pound of product

When the N-alkyl nitrophthalimide is prepared from an alkylamineaccording to the process of this invention, e.g., a butyl amine, theN-alkyl nitrophthalimide can be concentrated in an evaporator whereinessentially all of the strong acid can be removed.

The higher nitric acid solubility of alkylnitrophthalimides according tothis invention allows the alkylnitrophthalimide to remain in solution athigher solids levels during a falling film evaporator process. Water andnitrating agent thus can be removed to levels at which a more efficientliquid/liquid extraction or vacuum distillation can purify thenitrophthalimide product

As indicated earlier, the alkyl nitrophthalimide product that isprepared according to this invention is stable at temperatures at whichthey are liquid, and thus can be recovered and purified in liquid/liquidextraction processes, e.g., conventional extraction processes using hotaqueous solutions or hot alkali solutions such as bicarbonate solutionwherein a solution of the product is washed. The product also can bedistilled at high vacuum and condensed to give purified molten productIt is not possible to effectively employ either of these twopurification steps when synthesizing methyl-derived nitrophthalimides.Both processes are conducted at temperatures at which n-methyl-derivedproducts melt and decompose.

Purification of butylnitrophthalimides by liquid/liquid extractionpreferably comprises pretreating the butyl-derived material prior toextraction with concentrated acid, e.g., a small amount of concentratedsulfuric acid (acid that is about 95% by weight sulfuric acid), and thenwashing the treated material using dilute basic solution, e.g., about0.2-1% by weight sodium bicarbonate. The sulfric acid pretreatmentgreatly enhances the purity of the product over that obtained fromdirectly extracting such material. Without being held to any particulartheory, the pretreatment and wash removes a butyl nitrate ester impurityresulting from the nitration reaction. Removing that impurity improvesthe yield of bisimide in the displacement reaction.

The N-alkyl nitrophthalimide then is dried. Conventional N-methylnitrophthalimides are dried by partitioning the N-methylnitrophthalimide from a water slurry into toluene. The toluene solutionthen is concentrated to about 30% solids, i.e., the solubility limit ofN-methyl nitrophthalimide in toluene at 100° C. Residual water also isremoved by azeotropic drying during this concentration step, as water isvery detrimental to the displacement reaction which follows thenitration reaction.

When N-alkyl nitrophthalimides are prepared according to this invention,other drying steps can be used. Butyl-substituted nitrophthalimide ismolten at a temperature of about 95° C. and can be dried in a columnusing heat and/or vacuum to remove residual water. On the other hand, ifthe solvent based drying system similar to that employed for themethyl-derived nitrophthalimides is to be employed, the nitrophthalimidecan be dried under near solventless conditions, i.e., up to about 100%solids. As mentioned earlier, these solventless conditions are possibledue to the melting and enhanced solubility characteristics of theproducts containing alkyl groups having at least 3 carbon atoms. Themelting temperatures of the alkyl nitrophthalimides produced accordingto this invention are provided in Table 5. N-alkyl nitrophthalimidesprepared from preferred alkylamines, e.g., amines derived from alkylshaving 3 to 6 carbon atoms, have a melting temperature in the range ofabout 90 to about 135° C. and solubilities of at least about 11% byweight, and in a number of instances 50% or greater in toluene at roomtemperature. Once dry, the N-alkyl nitrophthalimide is further processedto prepare bisimide.

Bisimides are prepared through displacement reactions between theN-alkyl nitrophthalimide and salts of bisphenol compositions. Suitablebisphenol salts are those alkali metal phenoxide salts of the formula.

    R.sup.1 --(OM).sub.2

For instance, bisimides such as aromatic ether bisimides of the formula##STR3## are prepared by heating the alkali metal bisphenol salt aboveand an N-alkyl nitrophthalimide of the formula, ##STR4## wherein R¹ is aC.sub.(6-30) aromatic organic radical, M is an alkali metal ion, R is analkyl having at least 3 carbons, and preferably 3 to 6 carbons. Thereaction of the salt and substituted phthalimide can be carried out inthe presence of a nonpolar organic solvent and an effective amount of aphase transfer catalyst.

R¹ more particularly includes ##STR5## and divalent organic radicals ofthe general formula where X is a member selected from the classconsisting of divalent radicals of the formula ##STR6## --O--, and--S--, where m is 0 or 1, and y is a whole number from 1 to 5.

Some of the alkali salts of the above-described alkali phenoxide aresodium and potassium salts of dihydric phenols, for example,

2,2-bis-(2-hydroxyphenyl)pro pane,

2,4'-dihydroxyphenylmethane,

bis(2-hydroxyphenyl)methane,

2,2-bis-(4-hydroxyphenyl)propane hereinafter identified as "bisphenol-A"or "BPA",

1,1-bis-(4-hydroxyphenyl)ethane,

1,1-bis-(4-hydroxyphenyl)propane,

2,2-bis-(4-hydroxyphenyl)pentane,

3,3-bis-(4-hydroxyphenyl)pentane,

4,4'-dihydroxybiphenyl,

4,4'-dihydroxy-3,3,5,5'-tetramethylbiphenyl,

2,4'-dihydroxybenzophenone,

4,4'-dihydroxydiphenylsulfone,

2,4'-dihydroxydiphenylsulfone,

4,4'-dihydroxydiphenylsulfoxide,

4,4'-dihydroxydiphenylsulfide,

hydroquinone,

resorcinol,

3,4'-dihydroxydiphenylmethane,

4,4'-dihydroxybenzophenone,

and 4,4'-dihydroxydiphenylether.

Preferred nitrophthalimides are, for example,4-nitro,N-butylphthalimide; 3-nitro,N-butylphthalimide;4-nitro,N-hexylphthalimide; 3-nitro,N-hexylphthalimide;4-nitro,N-propylphthalimide; and 3-nitro,N-propylphthalimide.

One method of preparing bisimide is to bring to reflux a heterogeneousmixture of an aqueous solution of alkali metal bisphenoxide salt and anonpolar organic solvent having a boiling point of from 80° C. to 200°C. at 760 torr, with the removal of solvent until it can be recoveredsubstantially free of water. An effective amount of phase transfercatalyst also is employed. Nonpolar organic solvents, such as toluene,can dissolve up to about 0.05% by weight water without affecting itsclarity. Small amounts of residual water can therefore be readilydetected. In forming the heterogeneous mixture, the order of addition ofthe nonpolar organic solvent and the aqueous solution of the alkalimetal phenoxide salt is not critical. There is preferably usedsubstantially stoichiometric equivalents of alkali metal hydroxide andbisphenol in forming the alkali metal phenoxide salt; however, up to a0.5 mole % stoichiometric excess of alkali metal hydroxide can betolerated without substantially adverse results in the displacementreaction. Other methods for preparing the alkali metal hydroxide saltare described in U.S. Pat. No. 4,202,993.

The phase transfer catalysts suitable for the displacement reaction are,for example, tetrabutylammonium bromide, tetrapropylammonium bromide,tetrabutylammonium chloride, tetrabutylammonium fluoride,tetrabutylammonium acetate, tetrahexylammonium chloride,tetraheptylammonium chloride, Aliquat 336 phase transfer catalyst(methyltrioctylammonium chloride, manufactured by the General MillsCompany), tetrabutylphosphonium bromide, tetraphenylphosphoniumchloride, hexabutylguanidium bromide, hexabutylguanidium chloride,hexaethylguanidium bromide, and hexaethylguanidium chloride.

The phase transfer catalyst can be utilized at from 0.0005 equivalent to2 equivalents of the catalyst, per equivalent of alkali bisphenoxide andpreferably from 0.01 to 0.05 equivalent Nonpolar organic solvents whichcan be employed in the practice of the present invention include, forexample, toluene, xylene, chlorobenzene and benzene.

Another method of preparing bisimide employs dipolar aprotic organicsolvents, such as those described in U.S. Pat. No. 3,957,862 and U.S.Pat. No. 3,879,428, the contents of both incorporated herein byreference.

Reaction between the nitroimide and diphenoxide to produce the bisimidecan be effected under an inert gas atmosphere such as nitrogen at 5° C.to 100° C. under substantially anhydrous conditions and in the presenceof dipolar aprotic organic solvent such as dimethyl sulfoxide,N,N-dimethylformamide, N-methylpyrrolidine, N,N-dimethylacetamide, etc.Mixtures of such solvents with non-polar solvents such as toluene,chlorobenzene, etc. also can be employed. Reaction time can vary between1 minute to 100 minutes or more depending upon temperature, degree ofagitation, etc. A proportion of from 1.8 to 2.5 moles of nitroimide, permole of diphenoxide can be used.

While higher or lower amounts of the reactant will not substantiallyinterfere with the formation of the desired bisimide, about 2 mols ofthe nitrophthalimide per mol of the bisphenoxide salt preferably is usedin preparing the bisimide.

The bisimide can be recovered from the reaction mixture and purified bya variety of procedures. One procedure includes dissolution of thebisimide with an organic solvent such as toluene and then washing orextracting with alkali solution containing about 1 to about 5% by weightalkali, to remove by-products, e.g., monoimides, etc., and unreactedstarting materials.

When N-alkyl nitrophthalimides are prepared according to this invention,the displacement reaction can be carried out at high solids levels,e.g., at 30% by weight, as well as levels in which the reaction issubstantially solventless. The solubility of alkylnitrophthalimideshaving alkyl groups containing three or more carbon atoms allows suchsolids levels. That solubility also provides for the higher throughputof product in the displacement reaction. The solubilities of thesecompounds also allow for extractions of displacement reactionby-products at temperatures below the temperatures typically used withthe methyl-derived products. Savings in energy costs thus can berealized as well. The solubilities of various alkylnitrophthalimidesproduced according to this invention are tabulated in Table 5 below. Onthe other hand, and as mentioned earlier, displacement reactions usingN-methyl nitrophthalimide and, e.g., bisphenol-A disodium salt caneffectively only be run to about 20% solids in the reaction mixturebecause of the methyl-derived product's limited solubility in toluene at85° C.

Displacement reactions involving methyl-derived N-methylnitrophthalimide and biphenoxide salts, when such reactions are run atsolids levels of more than 20%, lead to products having unacceptableamounts of impurities, as well as incur increased costs due toprocessing the solid product which precipitates out of the reactionmixture at such solids levels. Reactions of biphenoxide salts withN-butyl-4-nitrophthalimide according to this invention, on the otherhand, substantially avoid these problems and allow for a substantiallypure displacement reaction product, e.g., product containing less than 1part per million 4-nitro-N-alkylphthalimide, and much more flexibilityin the displacement reaction.

When using solventless reactions according to this invention, thereaction product is washed at 95° C. with 0.8% alkali aqueous solutions,the alkali concentration of conventional wash solutions. The reactionproducts according to this invention also can be washed at lowertemperatures, e.g., 85° C. or less, by using alkali solutions havinghigher alkali concentrations, e.g., 5% by weight alkali.

The carbon atom content of the alkyl group on the nitrophthalimideaffects the displacement reaction as well. Propyl-derivednitrophthalimides, for example, are preferred in certain instancesbecause such nitrophthalimides are easier to purify, thus providing areactant that is more likely to produce a higher yield of bisimide. Thecorresponding nitrate ester discussed earlier with regard to thebutyl-derived nitrophthalimide is not found. Butyl-derivednitrophthalimides, however, are preferred in some instances because oftheir lower melting points and higher solubilities in the solventsdiscussed above for the bisimide reaction.

The bisimide resulting from the displacement reaction can be furtherprocessed for introduction to an exchange reaction by removing solvent,if any, to give molten bisimide. Solvent is removed using conventionalprocesses such as flashing off the solvent and holding the bisimide meltat approximately 260° C. This flashing step, however, need not beemployed if a solventless displacement reaction is conducted usingalkyls according to this invention. Moreover, the melt of bisimideprepared according to this invention can be held at lower temperatures,e.g., 100° C. for butyl-derived bisimides.

The exchange reaction can be conducted utilizing conventionaltechniques. Transformation of the bisimide preferably is carried outunder known conditions by reacting the bisimide in its molten state withaqueous phthalic acid solution and triethylamine as described in U.S.Pat. No. 4,318,857 to Webb et al., the contents of which areincorporated herein by reference. It is preferable to run this reactionat a temperature in the range of about 180° C. to about 240° C. Theresulting reaction product then is extracted with an organic solvent.The aqueous mixture then is stripped from the extraction solution torecover the bis(ether anhydride).

Other exchange techniques are described in U.S. Pat. Nos. 3,957,862 and3,879,428, both incorporated herein by reference. For example, thebisimide is hydrolyzed with base to a tetra-acid salt, which isthereafter acidified to the tetra-acid. The tetra-acid then isdehydrated to the corresponding aromatic bis(ether anhydride).

Hydrolysis of the bisimide to the tetra-acid salt can be effected underreflux conditions in the presence of a base such as an alkali hydroxide,including sodium hydroxide. Reaction time can vary from 1 to 24 hours ormore depending upon reactants, degree of agitation, temperature,pressure, etc. The organic amine by-product can be removed by standardprocedures, such as steam distillation, decantation (when butyl-derivedmaterials are used), etc. In addition, the rate of hydrolysis is greatlyaccelerated by carrying out the reaction at above atmospheric pressuresat temperatures in the range of from 100° C. to 220° C.

The tetra-acid salt thereafter can be acidified with a mineral acid,such as a dilute aqueous solution of hydrochloric acid, etc. Theresulting tetra-acid is dehydrated and recrystallized by standardtechniques, e.g., refluxing with a dehydrating agent such as aceticanhydride.

In order that those skilled in the art will better able to practice thisinvention, the following examples are given by way of illustration, andnot by way of limitation.

EXAMPLE 1 Synthesis of "Make-Up" N-Butylphthalimide

A 10-gallon stainless steel reactor equipped with a turbine bladeimpeller, cooling coil, distilling condenser, azeotropic separator,thermocouple probe and means to maintain a nitrogen atmosphere, wascharged with 15.335 kg (103.53 moles) phthalic anhydride. N-butylamine(7.663 kg, 104.57 moles) from a pressure vessel was slowly added to thereactor which was at room temperature, e.g., about 25° C. The resultingexothermic reaction between the amine and phthalic anhydride wascontinued until the temperature in the reactor rose to 90° C., at whichtime addition of amine was complete. The reaction mixture was thenheated, with removal of water, for a 5 hour period until the temperatureof the mixture reached 200° C. The reaction mixture then was maintainedat 200° C. for 2 hours. The resulting product was vacuum distilled at atemperature ranging from 150-155° C. and at a pressure of 20 mm, toafford a liquid which solidified. The melting point of the solid wasabout 34 to 35° C. and was produced at a 95% yield.

EXAMPLE 2 Synthesis of Nitro-N-Butylphthalimide

A 3-necked, 5-liter round-bottomed flask, equipped with a mechanicalstirrer, was charged with 4,259 g (67.6 moles) of 99% nitric acid. Tothe flask was added 524.9 g (2.58 moles) N-butylphthalimide as a liquidat such a rate as to keep the reaction temperature under 40° C. Theaddition of the N-butylphthalimide was completed in about a half hour.The reaction was then heated for six hours to 50° C. in a temperaturecontrolled water bath. The reaction product was then fed to a wiped filmevaporator that was heated at 100° C. and under vacuum (30 mm). The bulkof the nitric acid was distilled off and the liquid product, i.e.,4-nitro-N-butylphthalimide and 3-nitro-N-butylphthalimide in a ratio ofabout 25:1, was isolated as a liquid which rapidly solidified to about98% solids upon cooling in the collection vessel. Depending on theoperation of the evaporator, the residual nitric acid in the product wasless than 3% by weight, and was as low as 0.1% by weight

EXAMPLE 2A Alternative Synthesis of Nitro-N-Butylphthalimide

A 100-mL 3-necked, round-bottomed flask was charged with 67.6 g of 96%sulfuric acid and 20 g of N-butylphthalimide. An addition funnel wascharged with 7.36 g of 96% sulfuric acid and 8.4 g of 96% nitric acid.The reaction was run at 19.3% solids by weight. The reaction vessel washeated to 35-40° C. using an external water bath. When theN-butylphthalimide had dissolved in the sulfuric acid, thenitric/sulfuric acid mixture was added dropwise at a rate such that thetemperature in the vessel did not exceed 50-55° C. The addition time wastypically 0.5 hours. The vessel was maintained at 45° C. for at least 3hours at which time the reaction was determined by HPLC analysis to becompleted.

The nitration mixture was then poured into water such that the strengthof the sulfuric acid was 50% by weight. The mixture was heated to 100°C. and stirred for 5 minutes. The stirring was ceased and a two phaseliquid liquid system resulted. The bottom aqueous phase was drawn offusing a pipette. The organic phase solidified upon cooling to give a90-94% yield of nitro-N-butylphthalimide. The ratio of4-nitro-N-butylphthalimide to 3-nitro-N-butylphthalimide was 15-20:1.The product phase could then be purified using conventional procedures.

The above nitration reactants were also run at 30% solids, resulting in3% starting material and ₋₋ 1% of oxidation side products present in thefinal product. The same nitration run at 20% solids resulted in aproduct containing <0.1% starting material and 4-5% oxidation sideproducts (products where the butyl group had been oxidized yet containeda 4-nitro group on the aromatic ring). It is therefore desirable to runthe mixed acid nitration at 30% solids to minimize the amount of yieldloss through oxidation side chemistry. The unreacted N-butylphthalimidecan ultimately be recovered in the exchange loop. A 30% solids levelreaction can also be run by using less sulfuric acid.

The purified products can then be used in a phase transfer catalyzedreaction with BPA disodium salt to afford >98% butyl bisimide.

EXAMPLE 3 Liquid/Liquid Washing of Nitro-N-Butylphthalimide

About 500 g of product isolated from the wiped film evaporator inExample 2 was charged to a one liter jacketed resin kettle, equippedwith a mechanical stirrer. The product was melted by hot oil which wasrecirculated through the jacket at 110° C. A nitrate ester impurity,i.e., the nitrate ester of 4-nitro-N-(3-hydroxybutyl)phthalimide, thenwas removed by converting the impurity to its corresponding alcohol andremoving the alcohol with a basic aqueous wash. In particular, thenitrate ester impurity was converted to an alcohol by treating thematerial with a 95-98% by weight sulfuric acid at 100° C. for 1 min. Thesulfuric acid solution was added to the melted product in an amount ofabout 1% by weight. The product and converted alcohol were then washedby adding 500 mL of water at 100° C., agitating the components for 30seconds, and then allowing the settling, e.g., for about 5-10 minutes,and separation of the neat product and aqueous phases.

The product was then washed with 500 mL of 0.2% aqueous sodiumbicarbonate as described for the water wash above, with a final 500 mLwater wash following the bicarbonate wash. Products from additionalnitro N-alkyl phthalimide synthesis reactions were similarly washed withother dilute bases such as 0.1-2% aqueous disodium phosphate, 0.1-2%aqueous sodium carbonate and 0.1-2% aqueous sodium bisulfite.

The resulting washed product was then azeotropically dried with tolueneand was then used in a displacement reaction in which 10.0 g (0.0367mole) sodium salt of bisphenol A was reacted with 18.23 g (0.0735 mole)of nitro-N-butyl phthalimide in 28 g toluene containing 0.22 g of C₆ Bcatalyst. The reaction gave 98% bisimide.

When the above displacement reaction was run without removing thenitrate ester impurity from the butyl-derived materials, very low yieldsof about 30-70% bisimide were obtained.

Yield loss, e.g., about 2-10% by weight, also was experienced whenstronger, e.g., 2% by weight basic aqueous washes were used in thepretreatment step. The larger yield loss can be attributed to greaterproduct hydrolysis that occurs with more base.

EXAMPLE 4 Alternative Washing of Nitro-N-Butylphthalimide

The product isolated in Example 2 was again treated with sulfuric acid(1 wt % of 98% sulfric acid), but then dissolved in 0.1-1 volumeequivalents of toluene with respect to the volume of product and washedwith the aqueous sodium bicarbonate regents at 80° C. Yields of greaterthan 99% nitro-N-butylphthalimide were obtained.

EXAMPLE 5 Synthesis of Nitro-N-Propylphthalimide

N-propylphthalimide (50 g) was nitrated in 500 g 99% nitric acid toproduce 4-nitro-N-propylphthalimide under conditions described inExample 2.

The reaction product was precipitated into water and then collected byfiltration. The product then was liquid/liquid washed at 100° C. withthree 50 ml portions of water and then azeotropically dried withtoluene. The product (10 g) then was used in a displacement reaction asdescribed in Example 3 to afford propylbisimide in 87% isolated yield.

EXAMPLE 6 Distillation of Nitro-N-Butylphthalimide

Materials washed according to Example 3 were distilled in a distillationcolumn having one theoretical plate. The distillation was conducted attemperatures (and pressures) of 150° C. (0.1 mm), 170° C. (0.15 mm), and185° C. (2 mm). The distilled material from each distillation was thenused in a displacement reaction to give bisimide in yields ranging fromabout 97 to 99%.

The materials washed according to Example 3 also were distilled by usingKugelrohr distillation equipment. In the Kugelrohr distillation, 87.6 gof nitro-N-butylphthalimide was distilled at 190° C. at 1 mm to afford84.1 g of material, i.e., about a 96% product yield as described inExample 3. In a subsequent displacement reaction, the product distilledby the Kugelrohr distillation resulted in about a 97% yield of bisimide.

EXAMPLE 7A Synthesis of Butyl Bisimide

The following Examples 7A and 7B illustrate the preparation of ButylBisimide in dipolar aprotic solvent. For example, 22.8 g (0.1 mol) ofbisphenol-A, 300 mL of dimethylsulfoxide, 100 mL of toluene, and 16.0 gof sodium hydroxide as a 50% aqueous solution (0.2 mol) is heated toreflux under a nitrogen atmosphere using a Dean Stark trap for 5 hoursto remove the water from the system. The toluene is distilled from thevessel after the bulk of the water is removed until the temperature ofthe reaction mixture exceeds 145° C. In this way, dry bisphenol Adisodium salt is prepared. The reaction is then cooled to 50-100° C. Tothe dry salt solution is added 49.6 g (0.2 mol) of dry4-nitro-N-butylphthalimide under nitrogen. The reaction is stirred for30 minutes to 2 hours at 40-130° C., at which time the reaction iscomplete as determined by HPLC analysis. The reaction mixture is thenadded to 1 liter of water at which time the butyl bisimide precipitates.The precipitate is collected via filtration and dissolved in 100-200 mLof toluene at 80° C. The organic phase is washed with 25-50 mL of 1%aqueous sodium hydroxide solution at 80° C. to effect purification ofthe product The phase is separated and the solvent removed on a rotaryevaporator under reduced pressure to afford a 92-97% yield of purifiedbutyl bisimide (mp 91-93° C.), suitable for the exchange reaction.

EXAMPLE 7B

Alternatively butylbisimide is prepared from the use of bisphenol A(BPA) disodium salt prepared in toluene. For example a 3-necked,3-liter, round-bottomed flask is charged with 228.29 g (1 mol) ofbisphenol A, 1 liter of water and 2 moles of sodium hydroxide. Themixture is heated at 90° C. under nitrogen to effect solution of thematerial as BPA disodium salt. The vessel is then charged with 1.5liters of toluene, and the two phase system is brought to reflux withthe use of a heating mantle. Water is removed from the reaction vesselwith the use of a Dean Stark receiver. The bulk of the water is removedwhen no more water separated in the Dean Stark receiver. At this point,750 mL of the toluene is distilled from the reaction vessel, and then 1liter of dry toluene is added back to the vessel. Again, toluene isdistilled from the vessel (1 liter) to furnish a dry white slurry ofprecipitated BPA disodium salt in toluene. The percent solids of theresulting slurry is determined by taking a known weight of arepresentative sample of the material, removing the toluene viadistillation, followed by heating under vacuum (150° C., 1 torr), andfinally weighing the isolated amount of salt.

A portion of this salt slurry containing 10.0 g (36.8 mmol) is thencharged to a 250 mL, 2-necked, round-bottomed flask equipped with a stirbar, a Dean Stark receiver topped with a reflux condenser and means formaintaining a nitrogen atmosphere. The flask is also charged with 150 mLof dimethylsulfoxide (or dimethylformamide). The reaction vessel isheated with an external oil bath, and the toluene is distilled from thepot. Once the bulk of the toluene is removed the temperature of theflask is lowered to 50-70° C., then the flask is charged with 18.2 g(73.5 mmol) of 4-nitro-N-butylphthalimide. The reaction mixture isheated for 30 minutes to 3 hours at 40-100° C., whereupon the reactionis judged complete using HPLC. The reaction mixture is then worked up asin Example 7A to afford a 90-96% yield of purified butyl bisimide,suitable for the exchange reaction.

EXAMPLE 7C Synthesis of Butyl Bisimide

a. Reaction Having a 25% Solids Level in Solvent

Bisimide was synthesized according to the displacement process disclosedin U.S. Pat. No. 4,257,953. In particular, two molar equivalents of drynitro-N-butylphthalimide were reacted under reflux with 1 molarequivalent of a disodium salt of bisphenol A in toluene having 1 mol %phase transfer catalyst present The reaction was conducted for 1.5 hoursat 125° C. and a 25% solids level followed by dilute, i.e., 1% causticwashes.

b. Neat Reaction

One mole equivalent of dry bisphenol A disodium salt was reacted neat,i.e., solventless, with two equivalents of nitro-N-butylphthalimide inthe presence of 1 mole % phase transfer catalyst The reaction gave 94%yield of bisimide. The resulting product then was washed with dilutecaustic media.

EXAMPLE 8 Comparison of Prior Art Bisimide Synthesis and BisimideSynthesis According to This Invention

a. Prior Art Synthesis of Bisimide from 4-Nitro-N-Methylphthalimide andBiphenol

A 250 ml three-necked round bottom flask equipped with overheadmechanical paddle (teflon) stirrer, stopper and modified Dean-Stark Trapfitted with reflux condenser and nitrogen inlet was charged with 8.957 g(43.45 mmol) 4-nitro-N-methylphthalimide, 0.668 g (1.086 mmol, 2.5%catalyst) C6B catalyst, 0.500 g (3.242 mmol) biphenyl (as an HPLCinternal standard) and 91.2 ml toluene before purging with nitrogen for5 minutes. The Dean-Stark was modified to allow liquid to return fromthe bottom of the trap back into the reaction vessel. The trap wasfilled with calcium hydride sandwiched between a plug of cheeseclothbelow and glass wool above (to prevent calcium hydride from returning tothe reaction vessel). The calcium hydride facilitated drying of thereaction solution.

The contents of the reaction vessel were heated in a 150° C. oil bathand toluene was refluxed through the hydride for 50-90 minutes beforecooling to room temperature. The reaction vessel was stoppered andplaced in a glove box under a nitrogen atmosphere.

Biphenol disodium salt (5.000 g, 21.72 mmol), which was preweighed intoa sample vial, was then added to the reaction mixture. The vessel wascapped, removed from the glove box, reattached to nitrogen and heated toreflux in a 150° C. oil bath. The point at which the solution reachedreflux was defined at t=0 for kinetic purposes, and the reaction wasmonitored every 30 minutes via HPLC. The reaction was under reflux for2.5 hours. Aliquots (approximately 0.50 ml) were removed through thereflux condenser using a 1.0 ml disposable glass pipet, diluted with 3ml chloroform and 0.5 ml N,N'-dimethylacetamide and then filteredthrough a 0.45 micron frit prior to HPLC analysis. The reaction wasallowed to cool to room temperature before being further processed. Theproduct precipitated from the solution.

The solid from the toluene supernatant then was filtered, followed byrinsing with 50-100 ml toluene. The solid was air-dried on a Buchnerfunnel via suction for 40 minutes. The recovered solid weighed 14.69 gand contained about 3.0 g sodium nitrite. The solid was then slurried in50 ml 0.8% NaOH for 10 minutes, filtered and then rinsed on the filterwith 50 ml distilled and deionized water. The solids were then dried ina vacuum oven at a temperature of 110° C. and a pressure of 30 torr for3 hours. The recovered solid weighed 10.64 g, representing a 97.1% yieldof bisimide. The melting temperature of the solid was in the range of205-207° C.

b. Synthesis of Bisimide from 4-Nitro-N-Butylphthalimide and Biphenol

A 100 ml three-necked round bottom flask equipped with overheadmechanical paddle (teflon) stirrer, stopper and modified Dean-Stark Trapfitted with reflux condenser and nitrogen inlet was charged with 8.00 g(32.2 mmol) 4-nitro-N-butylphthalimide, 0.495 g (0.806 mmol, 2.5%catalyst) C6B catalyst, 0.400 g (2.59 mmol) biphenyl (as an HPLCinternal standard) and 16.4 ml toluene before purging with nitrogen for5 minutes. The Dean-Stark was modified to allow liquid to return fromthe bottom of the trap back into the reaction vessel. The trap wasfilled with calcium hydride sandwiched between a plug of cheeseclothbelow and glass wool above to prevent calcium hydride from returning tothe reaction vessel. The calcium hydride facilitated drying of thereaction solution.

The contents of the reaction vessel were heated in a 150° C. oil bathand toluene was refluxed through the hydride for 50 minutes beforecooling to room temperature. The reaction vessel was stoppered andplaced in a glove box under a nitrogen atmosphere.

Biphenol disodium salt (3.71 g, 16.1 mmol), which was preweighed into asample vial, was then added to the reaction mixture. The vessel wascapped, removed from the glove box, reattached to nitrogen and heated toreflux in a 150° C. oil bath. The reaction was allowed to reflux for 2.5hours before cooling to about 80° C.

The reaction product mixture was then washed using three 15.0 mlaliquots of an aqueous 0.8% (w/w) NaOH solution which had been preheatedto 85° C. The washes were allowed to stir for 15 minutes before removingthe aqueous layer via 10 ml pipet. The product biphenol bisbutylimidewas recovered using a Buchi rotary evaporator. About 9.0 g of productwas recovered with a corresponding yield of about 95%. The meltingtemperature of the product was in the range of 170-172° C. 95-99%isolated yields were obtained from reactions using 1.0-2.5%hexabutylguanidinium bromide as the phase transfer catalyst The reactionemploying this catalyst was run according to conditions disclosed inU.S. Pat. No. 5,132,423, the contents of which are incorporated hereinby reference.

c. Solubilities of Methyl-Derived Biphenol Bisimide v.Butyl-DerivedBiphenol Bisimide

The solubilities (and melting points) of butyl-derived bisimides andmethyl-derived bisimides were measured. The solubilities of thealkyl-derived materials below, i.e., bisalkylimides of biphenoldianhydride in toluene at 80° C. This temperature represents thetemperature at which the toluene phase of the displacement reaction iswashed with dilute NaOH.

As indicated in Table 1 below, the solubility of the methyl-derivedmaterial was equal to or less than 1% by weight in toluene. Becausecommercially viable processes are run at higher percent solids, themethyl-derived products precipitate out of the reaction mixture in thoseprocesses, thereby requiring the methyl-derived products to be isolatedby filtration, followed by slurry washes of the solid product Thehandling of solid products on the scale of commercial processestherefore incur inefficiencies.

                  TABLE 1    ______________________________________    Comparison of the Melting Points and Solubilities in Toluene    at 80° C. of Various Bisalkylimides of Biphenol Dianhydride                           n-    Parameter           Methyl   Ethyl  Propyl                                 n-Butyl                                        n-Hexyl                                              Cyclohex    ______________________________________    Point (°C.)           205-207  211    211   172-174                                        136   246-250    Solubility           ≦1%                    7%     5%    20%    >50%  .sup.b    in Toulene                   20%    ˜80%    at 80° C..sup.a    ______________________________________     .sup.a Solubililty is given in % solids = (weight of bisimide)/(weight of     bisimide + weight of toluene).     .sup.b The solubility was determined to be <5% solids in refluxing     toluene.

d. Purity of Methyl-Derived Biphenol Bisimide v. Butyl-Derived BiphenolBisimide

Solid impurities present in the reaction mixture for preparing bisimidescontaminated the solid bisimide product when the product precipitatesout of solution during processing and reflux. Many of these impuritiescannot be washed free of the product prior to the exchange reactionbecause the washing techniques are only effective for washing thesurface of the particles. As a result, the outcome of the exchangereaction is adversely affected when the bisimide product is introducedto the exchange reaction mixture. The bisimide product derived frombutyl materials do not incur these problems because the butyl-derivedproduct is soluble enough to remain in solution during processing atreflux. The butyl-derived product therefore is in solution therebyavoiding the costs of processing substantial amounts of solid products.The commingling of product with impurities also is minimized.

The analysis provided in Table 2 below is exemplary of the purity ofmethyl-derived bisimides of the prior art and butyl-derived bisimidesproduced according to this invention. The methods used to conduct theanalysis also are indicated below.

                  TABLE 2    ______________________________________    Comparison of Purities of Product Biphenol Bisimides    from Butyl vs. Methyl Processes    Component      Butyl Bisimide.sup.a                               Methyl Bisimide.sup.b    ______________________________________    Biphenolc      0           100-1000 ppm    4-Nitro-Np                 --    butylphthalimide.sup.c    4-Nitry-N-     --          500      ppm    methylphthalimide.sup.c    Monoimide.sup.c                   0           30-200   ppm    Nitride.sup.c  <1     ppm      200-400                                          ppm    Na.sup.d       12.6   ppm      >400   ppm    Fe.sup.d       2.1    ppm      e    Zn.sup.d       3.2    ppm      e    ______________________________________     .sup.a Butylimide prepared according to Example 8(b) herein.     .sup.b Methylimide prepared according to Example 8(a) herein.     .sup.c Measured by high pressure liquid chromatography (HPLC) vs biphenyl     internal standard.     .sup.d Measured by Inductively Coupled Plasma.     .sup.e Was not measured.

                  TABLE 3    ______________________________________    Effect of Reaction Concentration on    Displacement Rates and Yields    % Solids at    Which Reaction    Was Run   % C6B Catalyst                          HPLC Yield Isolated Yield    ______________________________________    15        2.5         74.9       74.2    20        2.5         82.6       82.1    30        2.5         87.3       89.9    40        2.5         96.5       96.0    50        2.5         98.0       98.3    ______________________________________

EXAMPLE 9 Exchange Reaction with Butylbisimide and Synthesis of BPADA

Two exchange reactions synthesizing bisphenol-A dianhydride ("BPADA")from bisphenol-A bisbutylimide, phthalic anhydride, triethylamine andwater were conducted. These examples illustrate that the alkylaminesaccording to this invention can be run at a solids level reaction higherthan that typical of prior art exchange reactions, e.g., less than 30%by weight solids. The higher solids reactions obtain higher throughputin the plant and lower phthalic anhydride ("PA") concentration inrecycle.

a. Reaction Having 44% by Weight Solids

The apparatus used for this exchange reaction was a one liter autoclavemanufactured by Parr Associates equipped with mechanical stirring, avent port with external valve, a sampling port consisting of a tubewhich extends nearly to the bottom of the inside of the vessel and anexternal valve, an addition port with valve, a pressure gauge, athermocouple well for measuring temperature and a safety pressurerelease valve. A stainless steel bottle with valves at both ends wasattached to the addition port. One end of the bottle was connected to ahigh pressure nitrogen line for the purposes of pressurizing the bottle.Both the autoclave and the addition bottle had thermocouple wells fortemperature measurement and were wrapped with heating tape which wasplugged into a variable transformer for temperature control.Additionally, the autoclave was placed on a hot plate which also wasused as a heat source.

Bisphenol-A bisbutylimide was prepared by imidizing 2 moles bisphenol-Adianhydride (BPADA) with 2 moles of freshly distilled n-butylamine inacetic acid. The reaction was run for five hours. Acetic acid wasremoved via distillation, followed by a toluene wash to azeotropicallyremove the last traces of acetic acid. The toluene/bisimide solutionthen was stripped of toluene on a rotary evaporator, thereby providing aviscous oil. The oil was dissolved in 3:1 ratio of ethanol/ethyl acetateat reflux and then cooled to produce white crystals having a meltingpoint in the range of 92-94° C. The bisimide was then eluted throughsilica gel using toluene as an eluant to provide, upon solvent removal,a white powder.

The stainless steel addition bottle was charged with 63.0 grams (0.100moles) of bisphenol-A bisbutylimide and purged with nitrogen. Theautoclave was charged with 88.872 grams (0.6000 mole) phthalicanhydride, 91.071 grams (0.9000 moles) triethylamine (TEA), and 104.12grams of water and then purged with nitrogen. The molar ratio ofphthalic anhydride to bisimide thus was 6 and the ratio of triethylamineto phthalic anhydride was 1.5. The reaction mixture contained 30% byweight water.

The autoclave and addition bottle were both heated to 210° C. beforepressurizing the bottle to a pressure greater than that in theautoclave. To the stirring autoclave mixture was then added the moltenbisimide from the addition bottle by opening the valve on the bottle.

Samples were removed from the sample port after 30 and 60 minutes forworkup and analysis. These samples were stripped of solvent by heatingthe samples for 5 minutes at 250° C. and 2-10 torr to remove volatilesand to ring close the tetraacid triethylamine salts to dianhydride andany residual amide acids to imides. The resulting materials were cooledto room temperature and analyzed to determine the percent exchange.

Equilibrium of the statistical reaction mixture was reached after 30minutes. The percent exchange was about 73-77%.

b. Reaction Having 54% by Weight Solids

The same apparatus and procedure used in the low solids level exchangewere used in the high solids level reaction. The addition bottle wascharged with 63.0 grams (0.100 moles) of bisphenol-A bisbutylimide,prepared as described for the low solids level reactions, and thenpurged with nitrogen. The autoclave was charged with 59.25 grams (0.4000mole) phthalic anhydride, 48.5767 grams (0.4800 moles) triethylamine(TEA), and 55.6 grams of water, thereby running the reaction with aphthalic anhydride/bisimide ratio of 4.0 and a triethylamine/phthalicanhydride ratio of 1.2. The exchange reaction reached equilibrium inabout 40 minutes, and resulted in about 58-62% exchange.

The advantage of the butyl system over the methyl system is that BuPl,butylimideanhydride and butylbisimide have a greater solubility intoluene than the methyl analogs. Therefore, the column extractionefficiency will be greater and result in increased hydraulic loading tothe column (increased throughput, almost doubled, and lower operatingcosts). Energy savings in stripping toluene also result

EXAMPLE 10 Zone Refining

The solventless purification of 4-NPBI was achieved through theimplementation of zone-refining methodology. The purification procedurewas performed by loading crude molten 4-NPBI (m.p.88-92° C.; pure 4-NPBIm.p. 94-95° C.) into a quartz (or pyrex) reactor tube, and allowing thedark yellow-orange liquid to solidify. The reactor tubes were 71 cm longwith an outside diameter of 11-14 mm and an inside diameter of 6-11 mm.The tube reactors were mounted vertically in a double-pass zone-meltingapparatus. The two furnaces were initially set at 89±1° C. Thepurification process was studied by heating in either the upward or thedownward direction. The heater transverse rate was set between 2 and 8inches per hour. The process was cycled through from 1 to 25 passes.

Under the reaction conditions, the major contaminants moved in thedirection of increasing gravity (downward): i.e.3-nitro-N-butylphthalimide (3-NPBI; m.p. 68-70° C.), N-butylphthalimide(N-BPI; m.p. 32-35° C.). However, the data indicate that some of themore highly colored compounds enrich in the direction the furnaces move:i.e. 4-nitro-N-(3-nitrooxybutyl)phthalimide (Bob3; m.p. 67-68° C.), and4-nitro-N-(4-nitrooxybutyl)phthalimide (Bob4). In general, theconcentrations of all the contaminants could be reduced such that thecrude 4-NPBI was greater than 99+% pure. Furthermore, the purifiedmaterials exhibited substantially lower YI values than did the initialcrude 4-NPBI.

Section A (Zone-Refining):

Crude 4-NPBI was melted (approximately 95° C.); the 4-NPBI was obtainedfrom one of the following sources: CRD pilot plant (mixed acid source),Mt Vernon Hot Nitric (no washes), or Mt Vernon Hot Nitric (Bobsremoved). The resulting yellow-orange liquid 4-NPBI was poured into a 1mm thick-walled quartz tube (o.d. 12 mm; i.d. 10 mm; length 71 cm); sixto eight inches of purified sand had been loaded into the reactor tubepreviously, to provide both a heat-up zone for the furnaces andsufficient room to attach the tube reactor to the zone-refiner. Thesample was added into the tube reactor until roughly a 6 inch head spaceremained. The liquefied material was allowed to solidify. The reactortube was then loaded into a table-top, vertical-mount, twin-pass-meltingapparatus. The reactor tube was capped with a nitrogen bubbler to allowfor any out-gassing within the reactor environment. The two furnaceswere initial set at 89±1° C.

The samples were heated in only one vertical direction at a time.Heating in either direction was found to have its own advantage ordisadvantage depending on the source of the 4-NPBI. The furnaces wereturned off during the recycle stage where they moved from the end of thereactor tube back to the starting point; heat-up and cool-down delayswere programmed into each run cycle such that the furnaces were close tothermal equilibrium before they began moving in either direction.Heating in both directions (ovens always on) was not examined. Thefurnaces traversed the reactor vessel at 4 inches per hour. A total of 3to 10 passes were examined.

Upon completion of the purification procedure, the color of thecrystalline 4-NPBI in the reactor was noted to range from white to lightyellow depending on its position in the reactor. Starting at the 4-NPBIapex, the material was analyzed in 4-6 inch sections using standard HPLCprocedures.

General Nomenclature/abbreviations Note:4-nitro-N-(3-hydroxybutyl)phthalimide (3-OH),4-nitro-N-(4-hydroxybutyl)phthalimide (4-OH), 4-nitrophthalimide(4-NPIH), and 4-nitro-N-(x-nitrooxybutyl)phthalimide (Bobx)

Run 1: Hot Nitric, No Bobs (MV 86-48; HN 4-NPBI pp.275)

The crude 4-NPBI (35 g; 0.134 mol) was melted and loaded into a quartztube reactor as described above. The tube reactor was loaded intozone-refining apparatus once the material had resolidified. The ovenswere initially set at 89±1° C. Heating was in the upward direction withan oven transversal rate of 4 inches per hour. After three cycles, theoven temperatures were raised to 95±1° C. Three more cycles werecompleted before the purification process was terminated; the progressof the purification procedure was via visual inspection. Sampling of thepurified 4-NPBI was at approximately four inch intervals along thereactor tube starting at the top of the purified solid. The sampleanalyses were as follow:

Initial Crude Mixture: (yellow-orange crystalline mass) 4-NPBI(95.434%), 3-NPBI (4.496%), INT C═C (0.057%), 3-OH (0.011%), and 4-NPIH(0.003%)

Samples 1 & 2: (light yellow crystalline solid) 4-NPBI (98.448%), 3-NPBI(1.497%), INT C═C (0.047%), and 3-OH (0.008%).

Sample 5 (above sand): (white crystalline solid) 4-NPBI (99.922%) and3-NPBI (0.078%).

Sample 6 (sand residue): (dark orange-yellow solid) 4-NPBI (71.829%),3-NPBI (27.896%), N-BPI (0.148%), INT C═C (0.093%), 3-OH (0.0207%),4-NPIH (0.014%), and 4-OH (0.007%).

A second attempt at purification of this material produced similarresults. For example:

Sample 5 (above sand; 2nd Run): (white crystalline solid) 4-NPBI(99.716%), 3-NPBI (0.219%), INT C═C (0.053%), 3-OH (0.009%), and 2-OH(0.003%).

Run 2: Hot Nitric, No Washes (MV)

The impure 4-NPBI (40 g; 151 mol) was loaded, run, and analyzed as inRun 1. The initial 4-NPBI mixture was found to have the followingcomposition: (orange solid mass) 4-NPBI (93.706%), 3-NPBI (3.991%),highly polar material (1.187%), 4-NPIH (0.180%), Bob3 (0.137%), 3-OH(0.110%), 2-OH (0.108%), and 4-OH (0.046%). After purification, theanalyses of the segments indicated the following:

Sample 1 (top): (light yellow crystalline solid) 4-NPBI (98.598%),3-NPBI (0.491%), Bob3 (0.259%), 3-OH (0.137%), 2-OH (0.060%), 4-NPBI(0.043%), and 4-OH (0.031%).

Sample 2: (light yellow crystalline solid) 4-NPBI (98.807%), 3-NPBI(0.155%), Bob3 (0.355%), 3-OH (0.179%), 2-OH (0.058%), 4-OH (0.020%),and 4-NPIH (0.018%).

Sample 5 (sand residue): (orange-yellow solid ) 4-NPBI (78.850%), 3-NPBI(15.940), highly polar material (3.264%), 4-NPIH (0.511%), 3-OH(0.249%), 4-OH (0.084%), and 2-OH (0.045%).

Run 3: CRD Pilot Plant, Mixed Acid Source.

The crude 4-NPBI (16 g; 0.064 mol) was loaded and run as per Run 1. Theinitial mixture was determined to contain the following: 4-NPBI(97.351%), 3-NPBI (2.058%), 3-OH (0.167%), and N-BPI (0.108%). Afterpurification the following compositions were found:

Sample 1: (White crystalline solid) 4-NPBI (99.287%), 3-NPBI (0.405%),3-OH (0.119%), and N-BPI (0.005%).

Sample 2: (White crystalline solid) 4-NPBI (98.028%), 3-NPBI (1.543%),3-OH (0.136%), and N-BPI (0.071%).

Sample 3: (Light yellow crystalline solid) 4-NPBI (97.221%), 3-NPBI(2.256%), 3-OH (0.113%), and N-BPI (0.120%).

Sample 4: (Light yellow crystalline solid) 4-NPBI (96.608%), 3-NPBI(2.224%), highly polar material (0.374%), 3-OH (0.507%), and N-BPI(0.127%).

Section B. (Displacement Chemistry):

General procedures for the displacement reaction: The toluene used forthe displacement reactions was distilled from sodium/benzophenone ketylimmediately prior to use. The disodium salt of bisphenol-A (BPA) wassupplied by General Electric as a toluene slurry. The removal of toluenewas accomplished by heating the salt under vacuum (1×10⁴ mm Hg). Thedrying temperature was raised incrementally, with a final drying stageof 160° for 8 hours; the dried salt was subsequently stored in a VacuumAtmospheres Dri Lab glovebox for further use. The 4-NPBI wasazeotropically dried using toluene, immediately prior to running thedisplacement reaction. The C6B (bis(tri-n-butylammonium)-1,6-hexanedibromide) was provided by the Five Starr Group, inc. and used withoutfurther purification. The HPLC conditions for the displacement reactionanalyses utilize an ODS-18 reverse phase Whatman column and a linearsolvent gradient program (solvent ratio initial V/V H₂ O:CH₃ CN of56:44; solvent ratio final 100% CH₃ CN). The total time for HPLCanalysis program was 24 minutes. An internal standard(1,3,5-triphenylbenzene; 285 nm wavelength monitor) was used tocalibrate each HPLC chromatogram. The following examples illustrate thegeneral reaction procedures:

Run 1. Zone-Refined Sample 1 (Apr. 9, 1990: Hot Nitric; No Washes)

A 50 ml round-bottomed two-necked flask equipped with a stir bar, refluxcondenser, and a nitrogen bubbler was used for the reaction. Thereaction flask was loaded with 2.8440 g (10.4 mmol) of zone-refined4-NPBI, 1.422 g (5.0 mmol) of BPA disodium salt, 0.0379 g (0.06 mmol) ofC6B, 0.1686 g of triphenylbenzene (standard), and 5 ml of toluene. Thereaction vessel was placed in an oil bath preheated to 140° C. Theoverall reaction mixture contained 45% solids. Aliquots were taken at 5min. intervals. Each aliquot was quenched into a solution (10 ml)derived from a mixture of acetonitrile (500 ml), methanol (50 ml), and aglacial acetic acid (5 ml). After 2h, HPLC analysis indicated that theconversion to BPA-bisimide had only reached 16%. It was later determinedthrough HPLC analysis that this particular zone-refined sample containeda nitrate ester (Bob3; 0.259%) detrimental to both the product rate andyield in the displacement reaction.

Run 2. Zone-Refined Sample 5 (nitrate ester removed (No Bobs): MV 86-48;HN 4-NPBI)

The reaction was repeated with a reactor vessel outfitted as in Run 1.The materials used were: 4-NPBI (1.6094 g; 6.4 mmol), BPA disodium salt(0.8834 g; 3.2 mmol), C6B (0.0236 g; 0.03 mmol), 1,3,5-triphenylbenzene(standard: 0.1498 g), and toluene (3 ml). The reaction mixture contained45% solids. It was heated at 140° C. Aliquots were taken and analyzed asdescribed previously. The displacement reaction was found to be completewithin 15 minutes. The solution work-up involved cooling the reactionmixture down to 80° C. The cooled solution was stirred for 15 minutes inthe presence of 5% NaOHaq (base wash); the organic to aqueous volumeratio was 4:1. The isolated yield of the desired product was 85%. Thismaterial produced a YI number of 6.4. The monoimide level was ca. 0.96%.

Run 3. Zone-Refined Sample 5 (2nd Purification run; Nitrate esterremoved as in Run 2 starting material)

The reaction was repeated with a reactor vessel outfitted as in Run 1.The materials used follow: 4-NPBI (1.58 g), BPA disodium salt (0.86 g),C6B (0.023 g), 1,3,5-triphenylbenzene (standard: 0.146 g), and toluene(2.5 ml). The reaction mixture contained 45% solids. It was heated at140° C. Aliquots were taken and analyzed as described previously. Thedisplacement reaction was found to be complete within 20 minutes; thereaction was stirred for a total time of one hour. The solution work-upinvolved cooling the reaction mixture down to 80° C. The cooled solutionwas stirred for 15 minutes in the presence of 5% NaOH aq (base wash);the organic to aqueous volume ratio was 4:1. The monoimide level was ca.0.96%.

The above clearly demonstrates that 4-nitro-N-butylphthalimide (4-NPBI)can be readily converted to an analytically pure grade of material,through the use of zone-melting (zone-refining) techniques. The purified4-NPBI was subsequently shown to undergo facile conversion to thebisbutylimide of BPA dianhydride in high yield. The resulting bisbutylbisimide exhibited color numbers (YI=6.4) comparable to those nowobtained for the bismethyl bisimide process, under current plantoperation.

From the above it has also been concluded that other solventless, meltmethods of purification of the 4-NPBI (or its analogues) such as meltcrystallization process can be employed commercially. In a meltcrystallization process, there will be no oven movement; hence, all theimpurities in the crude 4-NPBI will flow out the bottom of the reactor(no furnace tracking problems as with zone-refining).

                                      TABLE 5    __________________________________________________________________________    ALKYL GROUP vs PHYSICAL PROPERTIES    Alkyl Group              Methyl                  Ethyl                     Propyl                         Butyl                            Hexyl                                Dodecyl                                    i-Propyl                                        i-Butyl                                            t-Butyl                                                n-Octyl    __________________________________________________________________________    Imide MP.sup.1 =              133 78 66  35 37  65  84  95  61  --          BP.sup.2 =              275 273                     285 298                            327 --  296 275 279 --          Sol.sup.3 =              6.7%                  22 27  >70%                            24% 21  25  22  18  --    Nitro MP =              176 107                     102 92 95  89  133 128 127 88    Imide BP =              334 330                     325D                         290D                            --  --  320D                                        329D                                            --  --          Sol =              2.0%                  22 33  >50%                            34% 24  11  18  29  --    BPA.sup.4 -          MP =              147 148                     111 94 92  OIL 126    Bisimide          Sol =              20% @                  20 50  100                            100 100 44  --  --  --              80° C.    BP.sup.5 -          MP =              198.sup.7                  211                     207.sup.7                         170.sup.7                            135 137 170    Bisimide          Sol =              <1% @                  7% <1.sup.7                         20%                            >90%.sup.7                                100 <1  --  --  --    80° C.    Oxy.sup.6 -              265 -- --  116                            --  --  --  --  --  102    Bisimide    __________________________________________________________________________     .sup.1 MP = melting point in ° C.     .sup.2 BP = boiling point in ° C.     .sup.3 Sol = solubility in toluene at room temperature     .sup.4 BPA = bisphenol A bisimide     .sup.5 BP = biphenyl bisimide     .sup.6 Oxy = bisimide of oxydianhydride     .sup.7 These values are not the same as those for the materials     illustrated in Table 1. The discrepancies could be due to the level of     impurities in the different samples used to obtain these values reported     here.     -- = not determined     OIL = material was not a crystalline solid having a discrete melting     point. The material is simply a viscous liquid.

What is claimed:
 1. A process for preparing N-alkyl phthalimidessuitable for preparing bisimides and bis(ether anhydrides), comprisingreacting liquid alkylamine and liquid phthalic anhydride under N-alkylphthalimide formation conditions and recovering liquid N-alkylphthalimide.
 2. A process according to claim 1 wherein said alkylaminehas a boiling point temperature of about 48° C. to about 250° C.
 3. Aprocess according to claim 1 wherein the alkyl group of said alkyl amineis a C₃ -C₆ alkyl.
 4. A process according to claim 1 wherein the alkylgroup of said alkyl amine is n-propyl, n-butyl or n-hexyl.
 5. A processaccording to claim 1 wherein the liquid alkyl amine and the liquidphthalic anhydride are reacted at a temperature in the range of about150° C. to about 175° C.